The immune system is regulated by the production of a variety of proteins called lymphokines. Lymphokines are produced by T cells, and recent data suggests that these cells can be classified by their patterns of lymphokine production. (TH1/TH2). Another way of classifying T cells is by the T cell receptor type they possess, the majority of which possess the alpha/beta receptor, with a much smaller population possessing the gamma/delta receptor. The exact role that each cell population plays in the immune response is still unknown. I have developed a system using PCR by which purified cell populations can be analyzed, and their lymphokine production quantitated. Using this technique, along with cell transfer experiments into scid mice to study single T cell subsets in an in vivo system, we will set out to determine what role individual T cell populations play at various stages of the immune response, and how they use lymphokines to orchestrate it. Specifically, we intend to examine the response to mycobacterial infections and leishmaniasis, two infections in which differential lymphokine production are suspected to result in different responses to the infection by the host. Characterization of the regulation of lymphokine production will give us an understanding of how the host responds to infections to clear itself from invading pathogens. This will enhance our ability to optimize host defenses to clinical disease.